Not just blasting people with lightning and frost in the best high fantasy tradition -- but it does include that.
Hmm -- should she have sunlight related powers too? After all, "fair" is also weather. (Though her liking to be about in the sunny weather because she always likes the weather draws less comment, up to the point where someone's surprised that the storm loving girl likes sun, too.)
It will at least ensure that her mysterious background is highlighted. They know she's the local equivalent of a RPG sorcerer but this will establish she's not a storm one. Though her affinity for stone would also underscore that.
The point at which they learn her type is a crucial turning point, and somewhat complicated by the way that its logical consequence is the climax of the story.